Shielded spark plug



Nov. 29, 1949 L. F. HAHN SHIELDED SARK PLUG Original Filed March 17, 1941 Patented Nov. 29, 1949 UNITED STATES PATENT OFFICE SHIELDED SPARK PLUG Lewis F. Hahn, Hatfield, Pa.

Substituted for application Serial No. 383,725, March 17, 1941. This application November 25, 1946, Serial No. 712,227

1 Claim. (Cl. 123-169) The invention relates in general to spark plugs for internal combustion engines of both the airplane and automotive vehicle type, and the invention specifically relates to spark plugs of the radio shielded type. The present application is a substitute for forfeited application Serial No. 383,725, filed March 17, 1941.

The primary object of the invention is to provide an improved and simplified form of spark plug which will feature economy in manufacturing costs while meeting service requirements in the high pressure type of aircraft engine now in modern use and with these objects in view the invention features the providing of easily manufactured component parts; the minimizing in number of such parts and the providing of parts which can be readily assembled with other different size parts to provide for the fabrication selectively of spark plugs of different sizes and at the same time to provide a form of plug which can be assembled from the different size stock parts without necessity of using skilled labor in the assembly, or in the replacement of damaged or worn parts.

In spark plugs, particularly in the case of spark plugs of the shielded type designed for use in heavy pressure engines, difficulty has been experienced in taking off from the plug that more or less exact amount of heat under varying service conditions so that the plug in its firingarea will not run either too hot or too cold. Accordingly, the invention contemplates the providlng of a simplified form of heat radiating control which by the simple replacement of a variable size gasket, that particular gasket can be selected which will give the requisite degree of plug to the shell and to other associated heat radiating elements of the construction.

Incidental to the intent to provide for the minimum number of diiferent size component parts necessary to be carried in stock to meet the usual commercial demands for different size plugs, the disclosure features in its shell element the providing of means in the form of different lengths of spacing collars to provide at will either a. long or a short reach type of plug, Insofar as its central core assembly is concerned, the invention features cores designed to be of different sizes fashioned to fit in a standard form of shell, and the providin of different lengths of shielding barrels, any one of which can be screwed into the standard shell.

In its feature of economizing in manufacturing costs, the invention contemplates the formin of heat transference from the firing zone of the the shell and shielding barrel elements of standard hex stock to avoid the present expensive operation of forming squared faces as tool engaging nuts and to confine the machining to relatively inexpensive borings, threadings, and similar lathe operations, which can be cheaply done on automatic screw machines.

Further objects and advantages, not specifically enumerated above, will be apparent as the invention is described in connection with the embodiment illustrated in the accompanying draw ings.

In the accompanying drawings:

Fig. 1 is a view in axial section of a shielded spark plug constituting a preferred embodiment of the invention shown mounted in a head of an lntemal combustion engine; 7

Fig. 2 is a detached view partly in section of a known form of connector on an end of the cable harness shown in position about to be lowered into engagement with the spark plug of Fig. 1;

Fig. 3 is a detailed, enlarged perspective view of a combined heat conducting and gas sealing gasket shown in axial cross section in Fig. 1;

Fig. 4 is an end view of the lower, firing end of the spark plug shown in Fig. 1; and

Fig. 5 is an axial, sectional view of a modified form of shell and associated core assembly with associated spacing collars located between a head on the spark plug and the head of an internal combustion chamber into which the shell is screwed.

Referring to Fig. 1 there is disclosed a, shielded spark plug comprising primarily a shell ill in which is fitted a core assembly H held in place by a shielding barrel l2 and which plug is screwed into the plug opening extending through the wall A of the cylinder of an internal combustion engine.

The shell [0 was initially a length of tubular hex stock. The upper portion I3 is left unmachined for a portion of its length to form a length of section in the form of a hexagon to which wrench or other tool may be applied for screwing the spark plug into the cylinder head, or removing it therefrom. The lower portion of the stock material is twice reduced and its lower end threaded to form the cylindrical extension M for engaging the threads in the wall or head A of the firing cylinder. One end of the original bore of the stock length is machined to form an are shaped projection I5 which forms the outer electrode of a pair of coactin firin electrodes. The opposite or upper end of the bore is counterbored and threaded to form an enlarged cylindrical bore ii for receiving the lower threaded end of the barrel II. The mid-portion of the bore of the shell is machined to form a long conical core seat ll forming an included angle of about five degrees with the axis of the plug indicated by the line -4;. It is a feature of this disclosure that the seat ll be unusually long and at the same time provide a relatively long and narrow clearance I8 between the inner end of the shell and the core assembly so as to minimize the amount of hot gases which are passed up to the gasket of Fig. 3 as hereinafter described.

The core assembly comprises a centrally positioned conducting core element l9 and an insulating body of ceramic material. The conducting core element comprises a thin pencillike spindle 2|, the upper end of which is threaded as shown at 22 and therebeyond the extreme upper end of the spindle is turned down to a needie-like point forming a cable connector 23. The lower end of the spindle is provided integral therewith with an enlarged flat cylindrical head 24 forming the inner of the pair of electrodes and located within the outlines of the outer annular electrode IS.

The insulating body 20 is of somewhat bottleshape form, having a long frusto-conical body portion 25 and a long, thin upwardly extending cylindrical neck portion 26. The top of the body portion as it rounds into the neck portion forms a conical shaped shoulder 21. The body 20 is a one-piece molding and is held clamped between the enlarged head 24 at its lower end and a small nut 28 engaging the threaded end 22 at the upper end of the spindle. The insulating body portion 25 is received intermediate its ends in a gasket 29 of soft copper or other highly conductive material. This gasket, more particularly shown in Fig. 3, is of frusto-conical form having a relatively thinwall with its inner and outer faces formed to snugly fit the'body portion 25 and the seat ll respectively. This gasket may have a uniform thickness of wall section throughout and in this case it is designed simply as a gas seal and as a means for conducting heat from the core assembly to the shell.

In the form of the gasket herein illustrated, the wall 30 is formed of minimum radial cross section at one point 3| in its circumference, gradually increasing in radial thickness to the diametrically opposite point 32. Such a form of gasket may be rotatively adjusted on the core assembly to vary the opening of'the spark gap 33 formed between the inner and outer electrodes at the point where they approach each other most closely. By simply rotating the core assembly ll about its own axis as it is located in place as shown in Fig. i, any desired portion of the perimeter 34 of the inner electrode 24 may be brought to face the arc shaped projection i5, also by rotating the conductive sleeve of Fig. 3 as it is located on the core assembly, the width of the spark gap 33 may be accurately set.

It is a particular feature of the gasket as herein used that by virtue of its axial length it may be used to control the area of heat transference from the core assembly to the shell. It is accordingly intended that there b kept in stock gaskets of slightly varying length and, in assembling the parts to form any particular plug, that the length of gasket will be selected which is known to form a plug which will have neither too great nor too little heat radiation from the firing area adjacent the firing gap 33. In using such gaskets, it is the intent to maintain as much 4 length to the clearance l8 as possible so as to remove the gasket as far as possible away from the hot area at the firing electrodes and the gasket presents only a thin edge of material exposed to the hot gases in the combustion chamber of the engine.

The shielding barrel l2 was initially a long length of straight tubular hex stock having a bore of uniform diameter extending therethrough and which original bore is retained in the finished barrel, thus saving in cost of forming such barrels. Even if the bore of the original stock happens to be too rough, a simple straight reaming operation will be sufilcicnt to smooth the bore. In its mid-portion, the original stock was left unmachined for a short distance to form a polygonal section 35 resembling a nut by means of which the barrel can be screwed into place in the shell. The portion of the stock on one side of this section 35, that is, the lower end, is reduced and threaded to form the cylindrical lower end 36 for engaging the internal threads on the shell. The adjacent end of the barrel is beveled inwardly to'form a seat 31 having the same inclination to the axis a-b as the shoulder 21. The parts are so designed that as the barrel is screwed into the shell ID, the lower advancing bevelled end of the barrel engages directly against the shoulder 21 to force the body 20 downwardly and therethrough act on the gasket 29 to clamp the same firmly between the core assembly and shell to form the combined gas seal, heat conductor and heat regulator above referred to. It is also suggested that advantage may be taken of the fact that the gasket 29 (either form) is of soft copper, or equivalent soft metal, and is unusually long so as to insure the necessary large area of hermetically tight gas seal between the shell and core assembly.

As the barrel i2 is screwed into the shell i0 it forces the core assembly ii downwardly with a squeezing action on the soft gasket 29 which is thus clamped for its entire length between the conical surfaces of the core assembly and the shell. Even though the tapers of the gasket and the parts of the assembly and shell engaged thereby are intended to have an accuracy to interflt snugly as illustrated, nevertheless, as a practical matter minute variations from the ideal dimensions are inevitable in factory production. However, the thin shell, soft metal gasket 29 is capable under these conditions of being distorted both lengthwise as well as radially in both its external and internal dimensions by this squeeze action at least sufliciently to cause the gasket to conform itself automatically so as to take the shape imposed thereon by the pressure surfaces of the core assembly and shell engaging the same.

The gasket 29 is made of unusual length in order to provide sufficient area of engagemen between the core assembly and the shell to insure a non-leakage of the highly compressed engine gases past the same. In actual practice, the gasket is almost as long axially as is its mean diameter. As illustrated the axial length of gasket 29 is at least greater than one-half its mean diameter.

The lower edge of the gasket is unrestrained and is thus free to distend downwardly under pressure from the sleeve H to project more and more into the open clearance l8 with increase in the squeeze pressure thus tending to elongate the gasket axially at least slightly. With increase in length of course more and more area of heat transference is provided between the body portion and the grounded shell "I. It is a feature of this disclosure that there is no need of any gasket between the barrel and core assembly required of other similar devices.

The other portion of the barrel forming stock above the section is likewise reduced from its original hex form and threaded to form a long, upper portion 38 exposed for air cooling. The barrel extends for a material distance above the upper end of the cable connector 23. The threads at the upper end of portion 38 are designed to receive the swivel coupling nut 39 of a detachable connector 40 clamped to the end of a cable 4| carrying conductor 42 for supplying high tension current to the connector 23. Following conventional details in this connection swivel nut 39 is rotatively mounted on flange 2 of split sleeve l which is clamped about the usual metal braiding on cable 4|. The balance of the barrel below the threads utilized for the purpose of securing the cable in place is intended to provide an air cooled heat radiating surface 43. The fact that this portion 43 is threaded provides for an increase in heat radiating surface over what would be provided if this upper portion of the barrel were otherwise smooth. It has been found that there was no material addition in manufacturing cost in running the thread tapping die as far as possible along the barrel over what was necessary to provide for the cable connection and these extra lengths of threads contributed, at least to some extent, to the efliciency of heat radiation and air cooling of the barrel.

For the purpose of arranging the parts so that different size connectors, that is, different size nuts like nut 39, may be utilized, an adapter in the form of a thin external and internally threaded sleeve 44 may be screwed either into the coupling nut 39 as illustrated, or brazed, or otherwise secured to the upper end of the threaded portion 38 of the barrel.

A long sleeve 45 of insulating material is replaceably positioned in the bore of the barrel I2, preferably with a snug but sliding fit to form a lining to the barrel and to form a filler occupying substantially all of the space between the reduced upper portion 26 of the core assembly and the barrel. The sleeve is lowered into the barrel until its lower end is near the shoulder 21. The sleeve 45 projects above the upper end of the barrel and is provided at its projecting upper end with a groove 46 providing a means for conveniently gripping the sleeve in the act of inserting it into or removing it from the barrel. This sleeve is pre-formed and may be accurately molded to shape and size and it is herein suggested that it may be formed of ceramic or equivalent thermoplastic material.

As the ceramic core may equally be formed to accurate dimensions as an incident of its being molded to shape, the insulating sleeve can be made to form a snug fit thereon without necessity of preforming any work on it after it is initially molded. The upper end of the insulating sleeve provides a smooth bored opening for the insertion therein of the lower end of the intruded cable and acts to guide the cable conductor 42 into position to be engaged by the cable connector 23 at the upper end of the spindle 2|.

In place of the shell shown in Fig. 1, it is suggested in those cases where it is desired to use a. shell capable of functioning as both a long and short reach shell, to substitute therefore the shell 48 shown in Fig. 5. In this case, the upper end of the original hex stock is retained unmachined to form the hexagonal head 49. The portion therebelow is once reduced, forms a smooth cylinder 50 and therebelow the balance of the shell is threaded as shown at 5|. In the event that a long reach shell is desired, a relatively narrow collar or spacing sleeve 52 is located to encircle the smooth cylinder 50 beneath the external shoulder 53 defining the underside of the head 49 and the threaded portion of the shell is secured into the hole B therefore in the engine head or wall C.

In the event that a short reach shell is desired, another spacing sleeve 54 may be added to the sleeve 52 or, preferably, a single sleeve of the desired length is introduced between the shoulder head and the engine cylinder C. In either case, it is understood that that length of the spacing sleeve, and which also functions as a gasket, will be selected which will locate the lower or firing end of the plug in that position relative to the inner wall D of the engine cylinder which good practice indicates as being the proper location for the electrodes of the plug intended for that particular engine. Fitted in the shell is a core assembly 56 corresponding to the core assembly II and held in place by a shielding barrel l2 lined with an insulating tube 45.

It is within the scope of the disclosure to locate the spindle 2| concentric with the axis a--b, and to locate the axis of the head 24 slightly offset from the axis of the outer electrode l5.

The device illustrated provides an outer shielding and continuous conducting path for stray electric currents, from the shielded cable 4|, through the connector 40, through the barrel l2 and shell [0 where the pllug is grounded on the engine. Insofar as the plug is concerned, this outer shield is formed solely of two parts, a shell and a barrel screwed into the shell.

Considering the entire plug assembly it comprises only four major parts, the shell l0, barrel l2, core assembly II and insulating sleeve 45, constructed as separate units and assembled simply by inserting the core assembly into the shell,

screwing the barrel into place and slipping the insulating sleeve into the upper openend of the barrel.

It is within the scope of the disclosure and when maximum engagement of core and shell is desired in order to efiect maximum heat discharge to omit entirely the use of the heat discharging regulator 29 and to cause the core 20 to engage directly with its seat l1. Where a less degree of heat withdrawal from the core assembly is desired, that length of conical copper gasket either with uniform wall section, or variable as illustrated, will be selected from stock which previous experiments has shown to give the best firing conditions for the particular plug under observation and inserted in place preferably high up on the core assembly. In case of damage or worn parts, the coupling 45 and the shielding barrel are unscrewed, the damaged part which usually is the core assembly or the insulating sleeve is replaced and the parts rescrewed into place.

I claim:

In a spark plug, the combination of a shell provided with the outer of a pair of electrodes and with a conical shaped core seat, a core assembly adapted to be intruded into the shell and provided with the inner of said pair of electrodes, a tubular gasket of frusto-conical form fitted between the core assembly and said conical seat, said gasket having a wall of variable Number REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,128,819 Schmidt Feb. 16, 1915 1,155,515 Schmidt Oct. 5,1915 1,174,618 Schmidt Mar. 7, 1916 1,193,075 Schmidt Aug. 1, 1916 1,241,562 Schmidt Oct. 2, 1917 1,283,572 Schmidt Nov. 5, 1913 1,519,707 Russell Dec. 16, 1924 1,524,637 Cahill Feb. 3, 1925 1,675,764 Mickel July 3, 1928 1,789,719 Weatherhead, Jr. ...1 Jan. 20, 1931 1,929,202 Hahn Oct. 3, 1933 1,929,203 Hahn Oct. 3, 1933 1,940,324 Rabezzana Dec. 19, 1933 1,996,422 Hurley Apr. 2, 1935 1,999,117 Simsack Apr. 23, 1935 8 Name Date Cobb Aug. 27, 1935 Harper Dec. 24, 1935 Stemmlei Dec. 15, 1936 Nowosielski Feb. 22, 1938 Gm! Mar. 14, 1939 Nowosielski -1 Mar. 14, 1939 Ramsay Sept. 19, 1939 Carington Oct. 3, 1939 Nowoaielski Dec. 19, 1939 Hurley Apr. 23, 1940 Andres 1- Aug. 27, 1940 Rabezzana Apr. 15, 1941 Perkin Apr. 28, 1942 Devine Sept. 26, 1944 FOREIGN PATENTS Country Date Great Britain 1915 Great Britain 1928 France 1927 OTHER REFERENCES Dyke's Automobile and Gasoline Engine Encyclopedia-19th editi0n--TL145.D93. 

